LAREDO - With appearances on CNN and Nightline, Webb County Sheriff Rick Flores drew national attention to his role as top cop of a county on the front line against Mexican drug violence. But keeping that job comes down to a race that is decidedly local - full of harsh exchanges, nasty innuendo and Laredo's trademark tangle of conflicting loyalties. On Tuesday, Flores, 46, faces longtime state police official Martin Cuellar in a Democratic primary runoff, one of the area's hottest races in memory. His opponent's family name couldn't be more formidable - Cuellar, 49, is brother of U.S. Rep....